In-situ atomic-resolution observation of the anisotropic decomposition in TaN

The service life of transition-metal nitride thin films is critically limited by their tendency to decompose under extreme conditions. Previous studies have generally suggested that decomposition proceeds through a gradual structural transformation between different phases, accompanied by nitrogen loss. Here, using in-situ high-resolution transmission electron microscopy and quantitative measurements combined with theoretical analyses, we carefully investigate the decomposition behavior of a rock-salt TaN film at the atomic scale under electron-beam irradiation. The results reveal that TaN decomposes directly into metallic Ta without forming the intermediate hexagonal TaN 2 phase. Furthermore, when irradiated along the [0 0 1] TaN direction, TaN exhibits a stronger tendency toward structural transformation, while most nitrogen remains within the irradiated Ta product. In contrast, irradiation along the [1 1 0] TaN direction promotes nitrogen loss from TaN but suppresses the structural transformation. The observed decoupling between structural transformation and nitrogen depletion is primarily attributed to the orientation-dependent decomposition of TaN crystals. These findings provide new insights into the anisotropic decomposition behavior of transition-metal nitrides and establish a framework for tailoring the stability and composition of non-stoichiometric nitride systems.